[Lowfer] Has anybody tried...

[John Andrews]

Lyle,

> The specification sheet for the AD9850 DDS chip says that:
> "the output frequency can be digitally changed (asynchronously) at a rate
of
> up to 23 million new frequencies per second. The device also provides five
> bits of digitally controlled phase modulation, which enables phase
shifting
> of its output in increments of 180�, 90�, 45�, 22.5�, 11.25� and any
> combination thereof. "

Yeah, as I've discovered, there can be a lot of overhead in the control
software. I use the 9850 in my DDS exciter (not available as a kit <g>). It
is run by an 80C52-style controller, programmed in assembly code. When I
wrote the external "shift the phase by 180" routine, I just used my standard
frequency change routines, and they add a lot of overhead. I'm going to trim
the fat, and try to get the switching time to less than 1 ms. It's about
double that, right now. The DDS chip is not the issue, it's the programmer's
brain.

John A.